Indicating and measuring circuits



L.l SCHOTT INDICATING AND MEASURING CIRCUITS April 4, 1939.

Filed April 30, 1958 VVG.

ATTORNEYV Patented Apr. 4, 1939 UNITED STATE PATENT OFFICE INDICATING AND MEASURING CIRCUITS Application April 30, 1938, Serial No. 205,335

5 Claims.

The invention relates to indicating and measuring circuits and particularly to such circuits used in connection with two-way telephone systems for observing and recording data on their operation under service conditions.

To obtain proper operation of two-way telephone systems employing, at least over a part of the system, oppositely directed one-way paths for repeating the telephone signals in opposite directions, it has been found desirable in the past to utilize in connection therewith signal-controlled switching apparatus operating to effectively disable the signaling path for one direction while signal transmission is taking place over the signaling path in the opposite direction, in order to suppress echoes, prevent singing, and tominimize so-called double talking. The type and design of the switching apparatus and its adjustment is determined by the constants of the telephone circuits with which it is used and the variable service conditions encountered, such as circuit noise, static, etc.

An object of the invention is to determine quickly and accurately the talking conditions in such systems as a measure of the eiiciency of the switching apparatus.

This object is attained in accordance with the invention by an automatic device which, when connected to the telephone system under test will operate to indicate (l) when the subscribers are talking; (2) which subscriber is talking; (3) when both subscribers are talking at the same time (do-uble talking) and the number of times this occurs in a given interval, and (4) the number of circuit reversals in a given time.

Other objects and features of the invention will be brought out in the following detailed description thereof when read in connection with the accompanying drawing, the single ligure of which shows schematically a portion of a four-wire telephone circuit and associated therewith a service observation circuit embodying the invention.

The drawing shows schematically the west end of a known four-wire telephone circuit comprising the one-way transmission circuit EA including near its input the iilter l and the one-way ampliying device 2, for repeating telephone signals in the direction from west to east, and the one-way circuit WA including near its output the one-way amplifying device 3 and the attenuation pad 4, for repeating telephone signals in the direction from east to west, the input of the circuit EA and the output of the circuit WA being coupled by means of the hybrid coil HC and the associated balancing network N in conjugate relation with each other and in energy transmitting relation with the two-way telephone line TL in wellknown manner.

The remaining apparatus and circuits in the drawing make up the service observation circuit of the invention. As shown, it includes the three branch switching circuits A, B and C having their inputs respectively connected through high impedance resistance bridges across the input of the circuit EA, the output of the circuit WA and the network side of the hybrid coil I-IC.

Branch circuit A includes a voice-operated gain adjusting device `(vogad) of known type, shown within the dot-dash box 5, comprising an ampli- Y fier 6 used as a vario-repeater consisting oi two three-electrode amplifying tubes connected in push-pull, circuits for automatically controlling the gain of said amplier to compensate ior variation in the amplitude lead of impressed Waves comprising the gain decreaser circuit 'l and the gain increaser circuit 8, the three-electrode vacuum tube detector 9 having its input connected across the output of amplifier 6, and the operating winding I of the electromagnet relay T-l, connected in the plate-cathode circuit of detector tube 9.

The gain decreaser circuit 'I comprises the three-electrode vacuum tube detector Il having its input connected across the output of amplifier 6, and the regulating condenser l2 in the common portion of the control grid-cathode circuits of the two push-pull tubes in amplier 6. The tube Ii is arranged to operate in response to an increase in the output level of amplier 6 above a certain desired value to charge the condenser I2, so as to cause the gain of the amplier 6 to be decreased in proportion to the increase in the output level of amplifier t over the desired value. The gain increaser circuit 8 comprises an amplier-detector i3 having its input connected across the input of amplifier 6, and the electromagnet relay Ill in the output of device I3, operating in response to an increase in the level of the waves in the input of amplifier 6 above a certain minimum value to short-circuit the condenser I2 through the large resistance I3 so that the condenser will be slowly discharged thereby increasing the gain of ampliiier 6. As the gain increaser circuit tends to discharge the condenser I2 and the gain decreaser circuit tends to charge that condenser, the net effect is to produce a varying charge thereon which will be proportional to the amplitude level of the waves applied to the input of the amplifier 6 and such as to maintain the output level of the amplier at a substantially constant value. By proper choice of the constants of the vogad 5, this Vvalue is made such that when outgoing speech is applied from the circuit EA to the branch circuit A and is ampliiied and detected therein, the detected current in winding I of relay T-I will be such as to cause positive operation of that relay.

T'he branch circuit C comprises a voice-operated gain adjusting device (vogad) i6 including a vario-amplier and associated gain decreaser and gain increaser circuits, similar to the device in the branch circuit A, a three-electrode vacuum tube detector Il having itsinput connected to the output of the vogad I6, and the winding of the disabler relay D and an operating winding i3 of the relay R-I connected in series in the anode-cathode circuit of detector tube Il.

The branch circuit B connected across the output of the circuit WA comprises in order, the attenuation pad P, the vario-amplifier |9 comprising two three-electrode Vacuum tubes connected in push-pull, the three-electrode vacuum tube detector 2l! having its input connected to the output of amplifier |9,`and the winding 2| of the relay T-l, poled so as to oppose the operating winding lil thereof, connected in the cathodeanode circuit of the detector tube 2U. Condenser l2 controlling the gain of the vario-amplifier 6 in circuit A is also connected in the common portion of the control grid-cathode circuits of the tubes in thevario-amplier I9 of circuit B, so that the gain of the latter amplifier is varied in accordance with the condenser charge by the gain increased and gain decreaser circuits associated with the amplifier t under control of the outgoing speech signals lin path EA.

In addition to the opposing windings I and 2|, the relay T-l has a biasing Winding 22 supplied with biasing Ycurrent from the battery 23, which is `poled so as to oppose winding lil and thus assists winding 2| to hold the armature of relay T-l on its right-hand contact, as indicated, when winding 2| is energized. The relay R-| in addition to the operating winding I8 has a biasing winding 2li supplied with biasing current from the battery 25 in such manner as to hold the armature of the relay R-l normally on its righthand contact.

The talk direction indicator of the circuit of the invention shown within the dot-dash box so labeled, includes the relays T-Z and BF2, and the normally unoperated external circuits indicated by the lines E and F, respectively, controlled thereby, which may be lamp circuits or any other type of indicator, recorder, or alarm circuit. The winding of the relay'T-Z is supplied with energizing current from battery 26 through the normally closed armature and righthand contact of relay T-I, so that it is normally operated to hold its armature on its left-hand contact. The winding of the relay R-E is supplied with Venergizing current from battery 2l through the normally closed armature and righthand contact of relay R-l, so that it is normally operated to hold its armature on its left-hand contact. f

The double talk counter of the circuit of the invention shown within the dot-dash box so labeled, includes the control relays T-S and Pil-3, the chain of counting relays X, Y and Z, and the counter mechanism CM shown diagrammatically, which may be of any type suitable for progressively recording the number of times the relay Z is operated in a given time interval. The other elements of the talk direction indicator, the

double talk counter and the associated circuits, shown in the drawing will be referred to in the following complete description of operation of the Ycircuit of the invention.

put of the attenuator 4 in the path WA isrdiverted into the branch circuit B and the remaining portion is divided in the hybrid coil I-IC between the telephone line TL, and the network side of the hybrid coil I-IC where a portion passes into branch circuit C. Of course, if any unbalance exists between line TL and network N, a small portion of easts speech currents may reach line EA, as an echo. The portion of easts speech energy ltransmitted into the circuit C will be amplified by the amplifier in the vogad it therein, the speech energy in the input and output of lthe amplifier through the associated gain decreaser and gain increaser circuits operating to adjust the gain of the vogad I6 so that the level of the waves in the output thereof impressed on the input of the detector Il is of a desired constant value, in the manner which has been described above. The detected waves in the output of detector Il will be supplied as energizing current to the winding of the disabler relay D and the operating winding I3 of the relay R-l in series.

The disabler relay D will then operate to open its normally closed armature and contact to break the normal connection between the gain control condenser l2 associated with amplifier 6 of vogad 5, plate-cathode circuit of tube and its associated gain decreaser (o-utput circuit of tube Il) and gain increaser (ES, lli, l5) circuits, thereby preventing any changel in the gain of amplifier 6 and of the vario-amplifier in circuit B, under control of the waves reaching circuit EIA from WA by way of reflections from unbalances between line TL and network N.

The energization of winding i8 of relay R-l will overcome the bias on that relay through winding 2li, and relay R-l will operate to shift its armature from the right-hand contact to the left-hand contact.

The energy due to easts incoming speech entering the branchV circuits B and A respectively bridged across circuits WA and EA will be amplied by the amplifiers therein to an amount depending on the gain setting previously provided by the associated automatic volume control circuits, which gain will depend, of course, on the strength of the outgoing speech (from the west talker) only, and will be detected by the detectors 2@ and 9 in the respective branch circuits respectively causing energizing current to be supplied to the opposing windings 2| and'lil of relay T-l. Actual operation of the relay T-l on the incoming speech is prevented, however, because the energizing current supplied to the winding 2| by theV branch circuit B is slightly stronger than the energizing current supplied to the winding l from the branch circuit A so that the armature of the relay T-l is maintained on the right-hand contact of the relay as in the normal condition of the circuit when neither subscriber is talking.

The A branch circuit is less sensitive to incoming speech because of the loss encountered between the receiving and transmitting sides of the hybrid coil HC. The minimum difference between the A and B circuit sensitivity is set as small as possible by suitable selection of the value or the resistance pad P in the input of the circuit B for two reasons: (1) when the gain is high in the amplier S in circuit A, the loss provided by the pad P in the circuit B helps to prevent any unnecessary overloading of the following ampliiier-detector in the latter circuit; and (2) as will be pointed out below, the pad P provides a generally satisfactory operate margin for the relay T-l in favor of the outgoing or transmitted speech acting in the branch circuit A.

Relay T-l being in the normal condition shown, the relay T-2 controlled thereby will be maintained energized so that its armature will be held on the left-hand contact as shown. Relay R-l, however, being operated to the leithand contact, the normal energizing circuit for relay R-Z from battery 21 through the arma.

ture and right-hand contact of relay Rf-l will be broken, and the relay R2 will release so that its armature will fall back to the right-hand contact applying ground through the armature and normally closed right-hand contact of relay Y to operate the external circuit F to indicate to the observer that the east subscriber is talking. Similarly, the armature of the relay T-2 being in its normal condition on the relay lefthand contact, ground is not applied to the eX- ternal circuit E so that it is in the unoperated condition, which indicates to the observer that the west subscriber is not talking.

When the armature of relay R-I reaches its left-hand contact, the winding of relay R3 is energized by current from batteries 21 and 28 in series flowing through that winding, the series resistances 29 and 30 and the closed armature and left-hand contact of relay Rf-I. This will have no eiect on the operation of the counting relays X, Y and Z in the double talk counter circuit, for the first relay in that chain, relay X remains deenergized because its energizing circuit is broken at the left-hand contact of the relay T-3 because of the deenergized condition of the latter relay due to the fact that the control relay therefor, T-l, is unoperated.

When the east subscriber ceases talking, the removal of energizing current from the winding i8 of relay R-i will cause that relay to release to shift its armature from the left-hand to the right-hand contact thereby causing the relay BF2 to again return to the operated condition due to the resupply of energizing current to its winding from battery 21. This will again remove ground from the external circuit F indicating to the observer that the east subscriber is no longer talking.

Relay R-3 will remain operated for a short time interval after the relay Rf-l has released to break the connection of its winding through the latters left-hand contact to battery 21, while condenser 3l which was discharged to nearly the potential of battery 21 (which is negative with respect to ground) when relay Rf-I operated, charges up to the potential of battery 28 (which is positive with respect to ground) through the winding of relay R- and resistance 29 in series.

Now let it be assumed that speech currents from the west subscriber are being received at the west terminal of the four-wire circuit over the telephone line TL, and at that time no speech currents from the east subscriber are present in the output of the circuit WA of the four-wire circuit.

The speech energy from the west subscriber will be divided in the hybrid coil HC, half passing into the upper circuit EA toward the branch circuit A, and half passing into the lower circuit WA toward the branch circuit B. The portions of wests speech energy diverted into the two branch circuits A and B will be amplied by the amplifier and detected by the detector in the respective circuits causing energizing current to be supplied respectively to the opposing windings I0 and 2| of relay T-L Because of the effects of the attenuation pad P in the branch circuit B, the energizing current supplied to winding l0 of relay T-l from circuit A will be suiciently stronger than the energizing current supplied to the winding 2| from the branch circuit B, 4so that relay T-I will operate to shift its armature from the right-hand to the lefthand contact. If the hybrid coil HC is in normal balance the portion of the west subscribers speech energy which may enter the branch circuit C bridged across the net side of hybrid coil HC will not be suiiicient to cause operations in vogad IG or in relay R-l.

As soon as the armature of relay T-I leaves its right-hand contact, the source of energizing current 26 will be disconnected from lthe winding of relay T-2 and that relay will release shifting its armature from the left-hand to the right-hand contact thereby applying ground to the external circuit E indicating that the west subscriber is talking. Relay R-I being unoperated, the relay *Rf-2 will remain operated and ground will be removed from external circuit F, indicating to the observer that the east subscriber is not talking.

When the armature of relay T-l reaches the left-hand contact, energizing current will be supplied from batteries 26 and 32 through the series resistances 33 and 34 to the winding of relay T-3 causing the operation of that relay to close its armature and left-hand contact. This will not result in the operation of counting relays X, Y and Z as the energizing circuit for the rst relay in the chain, relay X, from battery 35 will still be broken at the left-hand contact of the unoperated relay R-3 because of the non-operated condition of the control relay R-I.

Now, let it be assumed that both the east and west subscribers are talking simultaneously, that is, there is double-talking. Then, both the relay T-l and the relay R-l will become operated in response to the energy entering the branch circuits A and C, respectively, causing the relays T-2 and R-2 controlled by the first-mentioned relays, respectively, to release, so that the armature of each is on the right-hand contact of the relay. This will cause ground to be applied to both external circuits E and F so that there will be no indication of which talking direction exists. Instead,V the double talk counter circuit will be operated in the manner which will be described and will remain so operated until the double talking stops and the circuit is again operating normally.

In the double talk counter circuit, the relay T-3 will be operated by the current from batteries 26 and 32 in series transmitted through the winding of relay T-3, the series resistances 33 and 34 and the closed armature and left-hand contact of the operated relay TI. Also, the relay R-3 will be operated by the current from batteries 21 ing, series resistances -29 and 30 and the closed left-hand contact and armature of relay R-l due Vto the operation ofthe latter relay.

A With both relays VT-t and R-3 operated, the winding of relay X is energized by current fromY battery 35 through the closed armature and lefthand contact of relay R-3 and the closed armature and left-hand contact ofrrelay T-3 in series, the series resistances 31 and 36, and the winding of relay X to ground. The condenser 38, normally discharged through the winding of relay X and resistance 36, becomes charged by battery 35 through resistance 37 before relay X is actually operated. Y

After a short delay due to the effect of the associated condenser-resistance arrangement, relay X will operate to close its armature and left-,hand contact completing an energizing circuit for the winding of relay Y from battery 39, the relay winding, series resistances 40 and 4I and closed left-hand contact and armature of relay X, and simultaneously causing the condenser 42, normally charged from battery,39 through the Winding of relay Y and resistance 40, to be discharged to ground. Relay Y will then operate to close its armatureand left-hand contact completing an energizing circuit for the winding of'relay Z from battery 43. Relay Z will then operate to operate the counter 44.

If, then, the west subscriber or the east subscriber, stops talking, the relay T|, or relay R-l will release, respectively breaking the energizing circuit for relay T-3 from battery 26, or for relay R-3 from battery 21. The latter relays, how ever, will not immediately release. VRelay T-3 would be maintained operated for a short hangover period while condenser was being charged up from battery 32 through the Winding of relay T-Srand resistance 33, and relay R-S would be maintained operated for a corresponding time interval While condenser 3l was being charged to the potential of battery 28 through the winding of relay R3 and resistance 29. Shortly following the release of either relay T-3 or R-3, relay X will also release. Release of relay Y is delay for a short period after the release of the preceding relay X While the condenser 42 is being charged up from battery 39 through resistance 40 and the relay winding. The slow release of relay Y obtained in the manner pointed out is provided to insure that one case of double talking, during which the R and T relays might chatter or operate and release several times, will not be counted more than once. Relay Z will release immediately when relay Y releases, releasing the counter CM. Each complete operation of both relays X and Y, which by proper design of the relay circuits may be made to occur onlyk when double talkingpersists for the selected time interval, will thus be registered by the counter.

In some'cases, as when the gain is high in the transmitting vogad 5 in branch circuit A and the incoming received speech volume is also high, the current in winding 2i of the relay T-'| received from the B branch circuit may be strong enough to prevent positive operation of the T-l relay through its winding Iii, when double talking occurs. The armature of the relay T-i would then chatter, operating and releasing generally quite rapidly as the combination oi transmitted and received speech energies acting in the B branch circuit varied. 'Io take care of conditions like this when chattering occurs, the short slow release periods of the relays R-3 and T-3 and the arsavca slow o`perate'action of relay X have been provided under control of their respective associated resistance-condenser arrangements. Thus, if the relays R-3 and T-3 are operated at anytime so that their operated periods overlap long enough to exceed the slow-operate time of relay X, a double talk situation may be assumed. Under normal operation of the circuit, when relays R-i,

R2 and T-i, T-2 are alternating in their actions with the east and west subscribers speech, respectively, the operated periods of relays R-B and T-3 do not overlap appreciably.

Thus, it is seen that the counter-mechanism CM, which may be of any suitable type, will Vgive an accurate indication of the niunber of double talks? occurring in a given time interval and the ,talk direction indicator comprising the relays T-Z and R-2 in combination with the eX- ternal circuits E 'and F, respectively,r Will give an indication of which subscriber is talking. The number of times the external circuits E and F are made operative in a given period of time Will indicate the number of separate ows of speech from the respective talkers. By other simple meansysuch as a non-biased polarized relay connected to operate and'remain in one position when` the ground pulses are applied from E and then to reverse its position when the ground pulses are applied from F, a count indication may Vbe `obtained of the number of telephone circuit reversals.

Various modifications of the circuits illustrated and described which are within the spirit and scope of the invention will be apparent to persons skilled in the art; for example,'as armeans of effectively preventing. false operation of the C branch circuit on outgoing speech, that circuit may be connected across the circuit WA in iront of the one-way amplifying device 3 instead of being bridged across the network side of the hybrid coil HC asI shown; other forms of vogads known in the prior art may be employed'in connection with the circuits A, B and C in place of the particular ones illustrated; and the number of counting relays and associated circuits used in the double talk counter may be varied if desired to change the double talking test period if the talking conditions warrant it. In addition to merely counting the number of times the direction relays operate, suitable clock mechanisms could be providedto measure the durations oi the various relay actions.

Y What is claimed is:

1. In combination with a two-way signaling system comprising at least over a portion of its length oppositely directed one-way paths for repeating signals in opposite directions, means for automatically indicating operating conditions in said systemcomprising means for effectively balancing the transmissions in the oppositely directed paths at one point in said system against each other, indicating means responsive in one manner to substantially stronger transmission in one of said paths than in the other and responsive in another manner to substantially stronger transmission in said other path than in said one path, and otherv indicating means operating Whenever transmissions of substantially equal strength are simultaneously present in said one and said other path for a given time interval, Y

2. In combination with a two-vvay signaling system including a four-Wire circuit, means for automatically indicating operating conditions in said system comprising means near one terminal of said circuit for effectively balancing the trans'- or L() mission in the outgoing side thereof against that in the incoming side, indicating means controlled by said balancing means responsive in one manner to substantially stronger transmission in said outgoing side than in said incoming side, and in another manner to substantially stronger transmission in said incoming side than in said outgoing side and other means for indicating Whenever transmission of substantially equal value is present in both sides of said circuit for a given time interval, and the number of times that condition exists during a predetermined time period.

3. 'I'he combination of claim 2, in which said balancing means comprises two control circuits respectively connected to said outgoing and incoming side of said four-Wire circuit, an electromagnetic relay having tWo opposing windings respectively energized in response to the transmis'- sion impressed on a different one of said control circuits, said control circuits and relay Winding being such that said relay will be operated in one direction in response to signal transmission in said outgoing side only and in the opposite direction for signal transmission in said incoming side only, the operation of said relay in said one direction controlling the first indicating means in said one manner and the operation in said opposite direction controlling it in said other manner, and said other indicating means comprising a third control circuit responsive to signal transmission in said incoming side and relay means jointly controlled by the first relay and said third control circuit When both are operated simultaneously for said given time interval and a counter controlled by said relay means for counting the number of simultaneous operations.

4. The combination of claim 2 in Which said balancing means comprising two amplier-detectors respectively controlled by the transmission in said outgoing side and in said incoming side of said four-Wire circuit, an electromagnetic relay having tWo' opposing windings respectively energized by the detected current from a diierent one of said ampliiier-detectors, and means for controlling 'the sensitivities of said ampliiierdetectors so that said relay will be operated in one direction When transmitted signals are present in said outgoing side and only dissipated energy of said signals in the incoming side and in the opposite direction When signals are present in said incoming side and only dissipated energy of said signals in said outgoing side, the rst indicating means being responsive in` said one manner to operation of said relay in said one direction, and in said other manner to operation of said relay in said other direction, and said other indicating means comprises a third amplifierdetector responsive only to signal transmission in said incoming side, relay means. jointly controlled by said third amplifier-detector and said relay and completely operated thereby When signal transmission exists simultaneously in said outgoing side and in said incoming side for said given time interval, and mechanism controlled by each complete operation of said relay means to count the number and duration of the complete operations in said predetermined time period.

5. A circuit for observing talking conditions in a four-Wire telephone circuit, comp-rising means for balancing the transmission at corresponding points in the two sides of said four-wire circuit against each other, and automatic means controlled by said balancing means for indicating at any instant the direction of signal transmission in said circuit, and the number of times telephone transmission occurs in both sides of said circuit for a given time interval.

LIONEL SCHOI'I. 

